1. Field of the Invention
The present invention relates to a backrest adjusting device for office chairs, and more particularly to a novel spatial design for a backrest and a headrest with the features of adjustable height, longitudinal buffer and angular rotation.
2. Description of the Related Art
Referring to FIG. 1 for a conventional office chair, the chair includes a stand 51 having a plurality of rollers, a seat cushion 52 fixed by an erected support rod, a backrest 53 installed vertically at the rear end of the seat cushion 52, and an arc streamlined headrest 55 pivotally connected to the backrest 53 by a plurality of insert rods 54. The height of the headrest 55 can be adjusted by fixing the positions of the insert rods 54 and the backrest 53. However, a problem of such structure resides on that the best leaning angle of a person's neck varies with each person's type of build, need and feel, when the person is sitting on a chair. Obviously, the design of the conventional fixed headrest violates these principles and definitely does not comply with practical applications.
Similarly, the structure of a backrest bump 56 of a conventional chair is connected by a transmission module (not shown in the figure) in the backrest 53 for indirectly driving a stand board in the backrest 53 for its extension and displacement. Since the driving position is situated at a lateral side of the backrest 53, the actual installation and operation of the chair greatly affect the overall stylish look of the chair, and the detached parts occupy much storage space when they are not in use. Further, the extensible and displaceable backrest bump 56 installed in the backrest cannot achieve the effect of supporting a user's waist or providing the elasticity for the backrest bump 56 due to the limitation by a too small driving extension and displacement. Further, the extensible and displaceable backrest bump 56 installed in the backrest 53 requires an extra transmission module to drive a stand board in the backrest 53 for the extension and displacement, and such arrangement incurs additional component and installation costs.
Therefore, it is a subject for the related industry and an expectation of consumers to overcome the existing shortcomings of the headrest and backrest of a conventional chair by providing an adjustable chair structure.